Ammonoids are an extinct group of marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs referred to as ammonites, are more related to living coleoids than they are to shelled nautiloids such as the living Nautilus species; the earliest ammonites appear during the Devonian, the last species died out in the Cretaceous–Paleogene extinction event. Ammonites are excellent index fossils, it is possible to link the rock layer in which a particular species or genus is found to specific geologic time periods, their fossil shells take the form of planispirals, although there were some helically spiraled and nonspiraled forms. The name "ammonite", from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble coiled rams' horns. Pliny the Elder called fossils of these animals ammonis cornua because the Egyptian god Ammon was depicted wearing ram's horns; the name of an ammonite genus ends in -ceras, Greek for "horn".
Ammonites can be distinguished by their septa, the dividing walls that separate the chambers in the phragmocone, by the nature of their sutures where the septa joint the outer shell wall, in general by their siphuncles. Ammonoid septa characteristically have bulges and indentations and are to varying degrees convex from the front, distinguishing them from nautiloid septa which are simple concave dish-shaped structures; the topology of the septa around the rim, results in the various suture patterns found. Three major types of suture patterns are found in the Ammonoidea: Goniatitic - numerous undivided lobes and saddles; this pattern is characteristic of the Paleozoic ammonoids. Ceratitic - lobes have subdivided tips, giving them a saw-toothed appearance, rounded undivided saddles; this suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous "pseudoceratites". Ammonitic - lobes and saddles are much subdivided. Ammonoids of this type are the most important species from a biostratigraphical point of view.
This suture type is characteristic of Jurassic and Cretaceous ammonoids, but extends back all the way to the Permian. The siphuncle in most ammonoids is a narrow tubular structure that runs along the shell's outer rim, known as the venter, connecting the chambers of the phragmocone to the body or living chamber; this distinguishes them from living nautiloides and typical Nautilida, in which the siphuncle runs through the center of each chamber. However the earliest nautiloids from the Late Cambrian and Ordovician had ventral siphuncles like ammonites, although proportionally larger and more internally structured; the word "siphuncle" comes from the New Latin siphunculus, meaning "little siphon". Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian and became extinct at the close of the Cretaceous along with the dinosaurs; the classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells' gas chambers.
While nearly all nautiloids show curving sutures, the ammonoid suture line is variably folded, forming saddles and lobes. The Ammonoidea can be divided into six orders, listed here starting with the most primitive and going to the more derived: Agoniatitida, Lower Devonian - Middle Devonian Clymeniida, Upper Devonian Goniatitida, Middle Devonian - Upper Permian Prolecanitida, Upper Devonian - Upper Triassic Ceratitida, Upper Permian - Upper Triassic Ammonitida, Lower Jurassic - Upper CretaceousIn some classifications, these are left as suborders, included in only three orders: Goniatitida and Ammonitida; the Treatise on Invertebrate Paleontology divides the Ammonoidea, regarded as an order, into eight suborders, the Anarcestina, Clymeniina and Prolecanitina from the Paleozoic. In subsequent taxonomies, these are sometimes regarded as orders within the subclass Ammonoidea; because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are rarely preserved in any detail.
Nonetheless, much has been worked out by examining ammonoid shells and by using models of these shells in water tanks. Many ammonoids lived in the open water of ancient seas, rather than at the sea bottom, because their fossils are found in rocks laid down under conditions where no bottom-dwelling life is found. Many of them are thought to have been good swimmers, with flattened, discus-shaped, streamlined shells, although some ammonoids were less effective swimmers and were to have been slow-swimming bottom-dwellers. Synchrotron analysis of an aptychophoran ammonite revealed remains of isopod and mollusc larvae in its buccal cavity, indicating at least this kind of ammonite fed on plankton, they may have avoided predation by squirting ink, much like modern cephalopods. The soft body of the creature occupied the largest segments of the shell at the end of the coil; the smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas. Thus, the smaller sections of the coil would have floated ab
A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus or nautilus. These marine animals are characterized by bilateral body symmetry, a prominent head, a set of arms or tentacles modified from the primitive molluscan foot. Fishermen sometimes call; the study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids; the class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses and cuttlefish. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Belemnoidea. There are over 800 extant species of cephalopod. An estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not fossilised. Cephalopods are found in all the oceans of Earth.
None of them can tolerate freshwater, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water. Cephalopods are thought to be unable to live in freshwater due to multiple biochemical constraints, in their +400 million year existence have never ventured into freshwater habitats. Cephalopods occupy most of the depth of the ocean, from the abyssal plain to the sea surface, their diversity is decreases towards the poles. Cephalopods are regarded as the most intelligent of the invertebrates, have well developed senses and large brains; the nervous system of cephalopods is the most complex of the invertebrates and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates. Captive cephalopods have been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs, return to their own aquarium; the brain is protected in a cartilaginous cranium.
The giant nerve fibers of the cephalopod mantle have been used for many years as experimental material in neurophysiology. Many cephalopods are social creatures; some cephalopods are able to fly through the air for distances of up to 50 m. While cephalopods are not aerodynamic, they achieve these impressive ranges by jet-propulsion; the animals spread their fins and tentacles to form wings and control lift force with body posture. One species, Todarodes pacificus, has been observed spreading tentacles in a flat fan shape with a mucus film between the individual tentacles while another, Sepioteuthis sepioidea, has been observed putting the tentacles in a circular arrangement. Cephalopods have advanced vision, can detect gravity with statocysts, have a variety of chemical sense organs. Octopuses use their arms to explore their environment and can use them for depth perception. Most cephalopods rely on vision to detect predators and prey, to communicate with one another. Cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size and horizontal or vertical orientation of objects.
The morphological construction gives cephalopod eyes the same performance as sharks'. Cephalopods' eyes are sensitive to the plane of polarization of light. Unlike many other cephalopods, nautiluses do not have good vision, they have a simple "pinhole" eye. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates. Given their ability to change color, all octopodes and most cephalopods are considered to be color blind. Coleoid cephalopods have a single photoreceptor type and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels; when camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment. They produce visual pigments throughout their body, may sense light levels directly from their body.
Evidence of color vision has been found in the sparkling enope squid, which achieves color vision by the use of three distinct retinal molecules which bind to its opsin. In 2015, a novel mechanism for spectral discrimination in cephalopods was described; this relies on the exploitation of chromatic aberration. Numerical modeling shows that chromatic aberration can yield useful chromatic information through the dependence of image acuity on accommodation; the unusual off-axis slit and annular pupil sha
Ventastega is a basal tetrapod that lived during the Famennian subdivision of the Late Devonian period 372.2 to 359.2 million years ago, though Ventastega origins as a tetrapod lineage are seated in the preceding Frasnian period of the Late Devonian when a surge of morphological diversification of tetrapods began. Ventastega is one of the earliest Devonian tetrapods yet discovered. Given two preferred orientations of the bones and the geological context in which Ventastega was found suggests a tidal-sea influence. However, like Tiktaalik, Ventastega was more aquatic than terrestrial, it had a large size for its period, with a length up to 1 m and a 20 cm skull. Per E. Ahlberg, a professor of evolutionary biology at Uppsala University in Sweden reported in Nature that limbs, not fins were attached to Ventastega; the fossils reported. They are 365 million years old. A skull and part of the pelvis of Ventastega curonica were found, they indicate it looked similar to a small alligator. The discovery contributes to the understanding of the evolutionary transition from fish to tetrapods.
Ahlberg, Per. E.. "Ventastega curonica and the origin of tetrapod morphology". Nature. 453: 1199–1204. Doi:10.1038/nature06991. PMID 18580942. Ventastega curonica at Devonian Times
An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms, it occurs. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty; these differences stem from the threshold chosen for describing an extinction event as "major", the data chosen to measure past diversity. Because most diversity and biomass on Earth is microbial, thus difficult to measure, recorded extinction events affect the observed, biologically complex component of the biosphere rather than the total diversity and abundance of life. Extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. Marine fossils are used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land animals.
The Great Oxygenation Event, which occurred around 2.45 billion years ago, was the first major extinction event. Since the Cambrian explosion five further major mass extinctions have exceeded the background extinction rate; the most recent and arguably best-known, the Cretaceous–Paleogene extinction event, which occurred 66 million years ago, was a large-scale mass extinction of animal and plant species in a geologically short period of time. In addition to the five major mass extinctions, there are numerous minor ones as well, the ongoing mass extinction caused by human activity is sometimes called the sixth extinction. Mass extinctions seem to be a Phanerozoic phenomenon, with extinction rates low before large complex organisms arose. In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five mass extinctions, they were identified as outliers to a general trend of decreasing extinction rates during the Phanerozoic, but as more stringent statistical tests have been applied to the accumulating data, it has been established that multicellular animal life has experienced five major and many minor mass extinctions.
The "Big Five" cannot be so defined, but rather appear to represent the largest of a smooth continuum of extinction events. Ordovician–Silurian extinction events: 450–440 Ma at the Ordovician–Silurian transition. Two events occurred that killed off 27% of all families, 57% of all genera and 60% to 70% of all species. Together they are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that became extinct. Late Devonian extinction: 375–360 Ma near the Devonian–Carboniferous transition. At the end of the Frasnian Age in the part of the Devonian Period, a prolonged series of extinctions eliminated about 19% of all families, 50% of all genera and at least 70% of all species; this extinction event lasted as long as 20 million years, there is evidence for a series of extinction pulses within this period. Permian–Triassic extinction event: 252 Ma at the Permian–Triassic transition. Earth's largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species.
The successful marine arthropod, the trilobite, became extinct. The evidence regarding plants is less clear; the "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of mammal-like reptiles. The recovery of vertebrates took 30 million years, but the vacant niches created the opportunity for archosaurs to become ascendant. In the seas, the percentage of animals that were sessile dropped from 67% to 50%; the whole late Permian was a difficult time for at least marine life before the "Great Dying". Triassic–Jurassic extinction event: 201.3 Ma at the Triassic–Jurassic transition. About 23% of all families, 48% of all genera and 70% to 75% of all species became extinct. Most non-dinosaurian archosaurs, most therapsids, most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments; the Temnospondyl lineage of large amphibians survived until the Cretaceous in Australia.
Cretaceous–Paleogene extinction event: 66 Ma at the Cretaceous – Paleogene transition interval. The event called the Cretaceous-Tertiary or K–T extinction or K–T boundary is now named the Cretaceous–Paleogene extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct. In the seas all the ammonites and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time; the boundary event was severe with a significant amount of variability in the rate of extinction between and among different clades. Mammals and birds, the latter descended from theropod dinosaurs, emerged as dominant large land animals. Despite the popularization of these five events, there is no definite line separating them from other extinction events.
The Cenozoic Era meaning "new life", is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and extending from 66 million years ago to the present day. The Cenozoic is known as the Age of Mammals, because the extinction of many groups allowed mammals to diversify so that large mammals dominated it; the continents moved into their current positions during this era. Early in the Cenozoic, following the K-Pg extinction event, most of the fauna was small, included small mammals, birds and amphibians. From a geological perspective, it did not take long for mammals and birds to diversify in the absence of the large reptiles that had dominated during the Mesozoic. A group of avians known as the "terror birds" grew larger than the average human and were formidable predators. Mammals came to occupy every available niche, some grew large, attaining sizes not seen in most of today's mammals; the Earth's climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, offset by the Paleocene-Eocene Thermal Maximum.
Cenozoic, meaning "new life," is derived from Greek καινός kainós "new," and ζωή zōḗ "life." The era is known as the Cænozoic, Caenozoic, or Cainozoic. The name "Cenozoic" was proposed in 1840 by the British geologist John Phillips; the Cenozoic is divided into three periods: the Paleogene and Quaternary. The Quaternary Period was recognized by the International Commission on Stratigraphy in June 2009, the former term, Tertiary Period, became disused in 2004 due to the need to divide the Cenozoic into periods more like those of the earlier Paleozoic and Mesozoic eras; the common use of epochs during the Cenozoic helps paleontologists better organize and group the many significant events that occurred during this comparatively short interval of time. Knowledge of this era is more detailed than any other era because of the young, well-preserved rocks associated with it; the Paleogene spans from the extinction of non-avian dinosaurs, 66 million years ago, to the dawn of the Neogene, 23.03 million years ago.
It features three epochs: the Paleocene and Oligocene. The Paleocene epoch lasted from 66 million to 56 million years ago. Modern placental mammals originated during this time; the Paleocene is a transitional point between the devastation, the K-T extinction, to the rich jungle environment, the Early Eocene. The Early Paleocene saw the recovery of the earth; the continents began to take their modern shape, but all the continents and the subcontinent of India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, the Americas were separated by the strait of Panama, as the isthmus had not yet formed; this epoch featured a general warming trend, with jungles reaching the poles. The oceans were dominated by sharks. Archaic mammals filled the world such as creodonts; the Eocene Epoch ranged from 56 million years to 33.9 million years ago. In the Early-Eocene, species living in dense forest were unable to evolve into larger forms, as in the Paleocene. There was nothing over the weight of 10 kilograms.
Among them were early primates and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as Paracrax; the temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the Circumpolar-Antarctic current between Australia and Antarctica formed; this disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles. This allowed mammals to grow to mammoth proportions, such as whales which, by that time, had become fully aquatic. Mammals like Andrewsarchus were at the top of the food-chain; the Late Eocene saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grass. The end of the Eocene was marked by the Eocene-Oligocene extinction event, the European face of, known as the Grande Coupure; the Oligocene Epoch spans from 33.9 million to 23.03 million years ago. The Oligocene featured the expansion of grass which had led to many new species to evolve, including the first elephants, dogs and many other species still prevalent today.
Many other species of plants evolved in this period too. A cooling period featuring seasonal rains was still in effect. Mammals still continued to grow larger; the Neogene spans from 23.03 million to 2.58 million years ago. It features 2 epochs: the Miocene, the Pliocene; the Miocene epoch spans from 23.03 to 5.333 million years ago and is a period in which grass spread further, dominating a large portion of the world, at the expense of forests. Kelp forests evolved, encouraging the evolution such as sea otters. During this time, perissodactyla thrived, evolved into many different varieties. Apes evolved into 30 species; the Tethys Sea closed with the creation of the Arabian Peninsula, leaving only remnants as the Black, Red and Caspian Seas. This increased aridity. Many new plants evolved: 95% of modern seed plants evolved in the mid-Miocene; the Pliocene epoch lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climactic changes, which led to modern species and plants; the Mediterranean Sea dried up for several million years (because the ice ages reduced sea levels, disconnecting the Atlantic from
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
Late Devonian extinction
The Late Devonian extinction was one of five major extinction events in the history of life on Earth. A major extinction, the Kellwasser event, occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, about 376–360 million years ago. Overall, 19% of all families and 50% of all genera became extinct. A second, distinct mass extinction, the Hangenberg event, closed the Devonian period. Although it is clear that there was a massive loss of biodiversity in the Late Devonian, the timespan of this event is uncertain, with estimates ranging from 500,000 to 25 million years, extending from the mid-Givetian to the end-Famennian. Nor is it clear whether there were two sharp mass extinctions or a series of smaller extinctions, though the latest research suggests multiple causes and a series of distinct extinction pulses during an interval of some three million years; some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of the Givetian and Famennian stages.
By the Late Devonian, the land had been colonized by insects. In the oceans were massive reefs built by corals and stromatoporoids. Euramerica and Gondwana were beginning to converge into; the extinction seems to have only affected marine life. Hard-hit groups include brachiopods and reef-building organisms; the causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean anoxia triggered by global cooling or oceanic volcanism; the impact of a comet or another extraterrestrial body has been suggested, such as the Siljan Ring event in Sweden. Some statistical analysis suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions; this might have been caused by invasions of cosmopolitan species, rather than by any single event. Jawed vertebrates seem to have been unaffected by the loss of reefs or other aspects of the Kellwasser event, while agnathans were in decline long before the end of the Frasnian. During the Late Devonian, the continents were arranged differently from today, with a supercontinent, covering much of the Southern Hemisphere.
The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, was drifting towards Gondwana, closing the Iapetus Ocean. The Caledonian mountains were growing across what is now the Scottish Highlands and Scandinavia, while the Appalachians rose over America; the biota was very different. Plants, on land in forms similar to mosses and lichens since the Ordovician, had just developed roots and water transport systems that allowed them to survive away from places that were wet—and built huge forests on the highlands. Several different clades had developed a shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns, lepidosigillarioid lycopsids, aneurophyte and archaeopterid progymnosperms. Fish were undergoing a huge radiation, the first tetrapods, such as Tiktaalik, were beginning to evolve leg-like structures. Extinction rates appear to have been higher than the background rate, for an extended interval covering the last 20–25 million years of the Devonian.
During this time, about eight to ten distinct events can be seen, of which two stand out as severe. The Kellwasser event was preceded by a longer period of prolonged biodiversity loss; the fossil record of the first 15 million years of the Carboniferous period which followed is void of terrestrial animal fossils related to losses during the end-Devonian Hangenberg event. This period is known as Romer's gap; the Kellwasser event, named for its locus typicus, the Kellwassertal in Lower Saxony, Germany, is the term given to the extinction pulse that occurred near the Frasnian–Famennian boundary. Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, the first event to be detected based on marine invertebrate record. There may in fact have been two spaced events here, as shown by the presence of two distinct anoxic shale layers; the Hangenberg event is found on or just below the Devonian–Carboniferous boundary and marks the last spike in the period of extinction.
It is marked by an overlying sandstone deposit. Unlike the Kellwasser event, the Hangenberg event affected both terrestrial habitats; the extinction events were accompanied by widespread oceanic anoxia. This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil in the USA; the Kellwasser event and most other Later Devonian pulses affected the marine community, had a greater effect on shallow warm-water organisms than on cool-water organisms. The most important group to be affected by the Kellwasser event were the reef-builders of the great Devonian reef-systems, including the stromatoporoids, the rugose and tabulate corals. Reefs of the Devonian were dominated by sponges and calcifying bacteria, producing structures such as oncolites and stromatolites; the collapse of the reef system was so stark that bigger reef-building by new families of carbonate-secreting organisms, the modern scleractinian or "stony" corals, did not recover until the Mesozoic era.
Further taxa to be starkly affected include the brachiopods, ammonites and acritarchs